French Spacing

The term "French Spacing" is best avoided altogether.

Printing in English-speaking countries almost universally used very wide sentence spacing throughout the 18th and 19th centuries (and earlier also, although I haven't researched the 17th century as thoroughly). In France however, the common practice was to use standard word spacing between sentences.  Or at most, an en quad, half as much as the em quad used in English texts.  In my casual review of French texts from the 19th century, I find that the most typical space is word spacing, but upon close examination I see that it is often used inconsistently within a single text.  What I assume they did is attempt to have even spacing, but during justification, if the spacing couldn't be made perfectly even, they would prefer to add the extra space between sentences.  This is a perfectly reasonable approach.

English references on typography during the 19th century hardly mention this at all.  One reference that does is "American Dictionary of Printing and Bookmaking," by Wesley Washington Pasko in 1894.  Even here though, in a long section on the differences between English and French printing, it makes absolutely no mention of sentence spacing.  It's only in the section on the em quadrat that he mentions this practice: "This quadrat is not used in France at the end of complete sentences, but the period is there followed by an en quadrat or by the space of the rest of the line."

Example of word-sized spacing between sentences in a French publication.  From "Essai sur la Typographie" (1854), Ambroise Firmin-Didot.

Notice that in that description, the term "French spacing" is not used at all.  Nor does it appear as an entry in Pasko's dictionary.  The same is true of John Southward's Dictionary of Typography and it's Accessory Arts.  There is no entry at all about "French spacing".  In fact the earliest reference I can find at all to this phrase is another Southward book, Modern Printing Volume 1, published in 1915 (I have not been able to see the 1899 edition of this book).  In this book, the index does in fact list "French spacing".  But when you refer to the page in question, that phrase is not used at all.  Again in the context of the em quad and it's use between sentences, Southward simply says "French book printing forms an exception to this."

It isn't until 1939 that I find this phrase used in a text. The Complete Desk Book, by Christopher Orlando Sylvester Mawson and John William Robson describes French versus American spacing:

"French spacing and American spacing refer to the amount of space between sentences. In the former only a spaceband follows the period. In the latter there is an en quad plus the spaceband."

Note that "spaceband" refers specifically to Linotype's automatically justifying space element, i.e. a word space.  The timing of this term appearing is interesting because in 1939 the transition to "French" spacing in America was in full swing, and would be mostly the norm in books, magazines, and newspapers within ten more years.  This makes sense when you think about it.  When wide sentence spacing was so ubiquitous in English language printing,  you'd hardly need a phrase to differentiate between different styles.  Only when both styles were common in our culture was it necessary to have phrases to describe one or the other.

And this sowed the seeds of confusion.

Fast forward thirty or more years, and people in America are so used to seeing "French" spacing that it no longer makes sense to refer to it as French.  And so, inevitably, the term flip-flopped, or at least it tried to.  The first chink in the armor that I can find is in 1977.  In "Don't Call It Cold Type" by Frank J. Romano, he describes French spacing as using a thin space after sentences in addition to the word space.  This would be slightly wider, although nowhere near as wide as was common in English texts.  This is almost factually correct, since the French would traditionally use a thin space before the period where English texts did not.  However it seemed that Mr. Romano meant that in English we use only a word space, where the French used a word space plus a thin space.

Mr. Romano accelerated things in 1984, in "The TypEncyclopedia".  Here his error is more explicit:

"Additional space at the ends of sentences is called French spacing, a very old practice, commonplace in books up through the nineteenth century."

He's completely reversed the meaning of French spacing, relative to English/American spacing.  Still, this was an isolated mistake.  It was repeated again in 1986 by Printing Abstracts, Volume 41:

"'French spacing' is the typographic equivalent of placing two spaces after end-of-sentence punctuation.  It adds to reader comprehension and legibility, but is currently somewhat out of vogue."

Another isolated event.  But in 1994, I find three separate references by different authors, all making this same error: "Glossary of Typesetting Terms," Richard Eckerseley; "The Best 1001 WordPerfect Tips Ever," Mary V. Campbell, and "Step-by-Step Graphics, Volume 10".  To be fair, the majority of references still get it right relative to the original meaning and history.  But after 1994, the floodgates seem to be open, and the reversed meaning appeared in numerous books.

This reversal was probably inevitable.  Americans tend to sneer at the French, and anything "French" besides French Fries tends to be frowned upon.  So how could standard practice here ever be described as "French".  It's culturally inconsistent.  Calling the more alien practice of wide sentence spacing "French" feels more correct.

So where does that leave us now?  Modern references are a complete mess, with many still describing the original meaning, while many others use the reversed definition.  It's difficult to tell who is "winning" at this point.

In my opinion, we should simply stop using the words "French" and "English" in describing spacing.  They were never really used at all during the period of time where they were descriptive of common practice.  And there's very little chance of successful communication when using them.  For "English spacing" (the original meaning), "wide sentence spacing" is a nice drop-in replacement.  There's no clear winner for "French spacing", although "narrow sentence spacing" isn't awful, but it doesn't really clarify that the sentence spacing matches the word spacing.  Another option is "word-spaced sentences".  Or just explain in a complete sentence that you mean that sentences do not have extra space.

Spacing in Twitter (a small victory)

I tweeted this back in January to twitter's feature suggestions account:

Wide Spacer @WideSpacer 05 Jan 13

@features Please change the CSS for tweet text: set white-space to pre-wrap. With only 140 chars, if people use two spaces they mean it.

(The short answer is that sometime recently they have done exactly this.)

There was more going on than just the wishful thinking.  In fact many twitter clients, particularly those widely used on mobile platforms, already preserved both the spaces and the newlines in tweets.  So users of those clients could "format" their tweets with extra spaces and new-lines, and often did.  But on twitter.com, these formatting efforts were lost to HTML's default behavior of treating all new-lines as blank spaces, and of combining multiple spaces into a single space.

HTML doesn't do this because it hates spaces, or because it has taken sides in the debate on sentence spacing.  HTML was originally based on SGML, a markup language for adding meta information (like formatting instructions) to plain text.  In SGML's view of the world, spaces are not content.  They simply serve to separate words from each other.  One space does this just as well as ten spaces.  If there's any formatting to be done, that should be in a tag as meta information.

Of course HTML has never added any explicit formatting capability for sentence spacing (although there are plenty of workarounds, most of them cumbersome).  But HTML has always had a <pre> tag, which means the contents of the tag are pre-formatted, and no formatting should be done; the original spacing and new-lines should be displayed.

As the web progressed, and CSS became the standard way of doing things, a CSS property called "white-space" was added.  This property describes how spaces and new-lines should be interpreted.  The possible settings include "normal", which means the way HTML has always done things, and "pre" which means the text should behave just as it would inside a <pre> section.  It also includes the setting "pre-wrap" which is alot like "pre" except that lines are wrapped both as needed, and also on new-line characters.

The pre-wrap setting is perfect for twitter, where it will preserve the user's original spacing as much as possible, but still wrap lines as needed to fit into the available space.

(Also note that there's an obvious missing feature from "white-space": there is no setting which honors multiple spaces, but ignores new-lines.  This would be handy for people who have been writing HTML in some traditional editors where long lines that wrapped are inconvenient, e.g. the traditional UNIX "vi" visual editor.  They may want to preserve spacing but not the new-lines.)

A few weeks ago I began noticing that tweets on twitter.com were appearing showing user formatting.  A quick look showed that they had indeed changed their white-space property for tweet text to "pre-wrap".  So now tweeters can add their wide spacing and it will actually display properly for the majority of twitter users.

This also means the next time there's a twitter debate about sentence spacing, the monospacers won't be able to say "yeah but why doesn't your tweet have wide sentence spacing?"  Because now it will.

Thank you Twitter!

Type Was Made to Read

"Type," said the Foreman, "was made to read,
And that is a maxim it's well to heed,
For the printer frequently gets a start
With a Craze for 'beauty,' a bug for 'art,'
Which holds him fast in a fearful gripe
And keeps him trying mad stunts with type,
With seventeen fonts and seventy styles
And borders by thousands and rules by miles.

"Type," said the Foreman, "was made to read,
But the printer, oftentimes, in his greed
For novel features and 'class' and 'tone,'
Forgets this fact he has always known
And sends out work that is fine to see
And 'smart' and 'natty' as it can be,
A job with a swagger and high-bred look,
But hard to read as a Chinese book!

"Type," said the Foreman, "was made to read,
And that should serve as the printer's creed,
For work on the Linotype machine
Or hand-set jobs should be clear and clean,
Not ornamental, obscure, bizarre,
Composed of all of the fonts there are,
But simple, legible, quiet, plain,
A joy alike to the eye and brain!

For art in printing is not the way
Of wild extravagance, weird display,
But rather the unobtrusive thrall
Of type that gives you no shock at all,
But draws your eyes to the page with zest
And holds your mind to the thought expressed;
We must keep ourselves to this simple creed,
Type was made and is meant to READ

Berton Braley, Linotype Bulletin, March 1915

The Cost of Printing Errors on the Linotype

My central hypothesis on the demise of sentence spacing is that the Linotype was the major factor, due to the excessive cost of correcting errors (especially spacing errors), and because the apparent drop in quality with the Linotype could be alleviated with closer spacing.  My blog post "A River runs Through It" covers some of the quality issues.

The problem of expense comes into play in a few different ways, but the most significant was in error corrections, where you couldn't simply change out a letter or two.  You'd have to recreate the entire line from scratch in the best of cases.  In the worst cases, your correction affects spacing enough that the change affects other lines, and you have to recreate several lines from scratch, all for what might simply be the insertion of an extra space.

Anyway, I've come across a discussion of the Merganthaler Linotype machine in Hearings Before Subcommittee of House Committee of Appropriations (for an 1898 appropriations bill), which covers both the expense of errors and and the problems with quality.

Statement of Mr. Th. E. Benedict, Public Printer
  [...]
The Chairman. Let me ask you.  If you avail yourself of modern methods of composition, take for instance, the Merganthaler process?
Mr. Benedict. I can say this: I believe that the working force of the office, if the question were put to them, would say the present Public Printer has largerly added labor-saving machinery to the Goverment Printing Office.
Mr. Sayers. You have not gone to the full length that private institutions have done in the matter of labor saving machinery, have you?
Mr. Benedict. I have gone to the length I was able.  I have not been remiss in putting improved machines in the Government Printing Office which I thought would be useful and to the limit funds for such were available.
Mr. Sayers. I am not saying you have not done your full duty, but I am simply comparing the conditions of the Printing Office with private institutions?
Mr. Benedict. If it was a question as to whether the Merganthaler or Linotype was profitable to be used in the Government Printing Office, I have an opinion; but perhaps you do not care anything about that.
Mr. Stone. Do you use any of these machines?
Mr. Benedict. No; but I am very familiar with the machines.  I know there is a great humbug about the matter of profit of these machines as operated generally.  You need not put this down—I know the conditions under which they can be made profitable, and I know the conditions in many offices where they are unprofitable, and those are the conditions which would operate in the Government Printing Offices.  Outside of the Congressional Record we receive scarcely any copy which, when in type pages, is ready for the press.  Our page proofs are edited and reedited by you and other editors, and we reset the matter again, and when you have to reset a whole line or a page to correct an error of a letter or a word of the compositor or author, the work is very expensive, and such corrections with the Linotype machine are necessary, as it sets type on a slug, and to take one letter out you have to set every letter of the slug line, and to insert a long word or a few words you have to run over the whole sentence.
    If you have perfect copy, the Linotype machine is profitable, and if you do not have good copy it is not.  Under these conditions the typographic appearance of every daily newspaper in the country where such machines are used has been so lowered that they have ceased to be respected by persons of taste, and the typographical errors and lack of typographical taste are due to the use of the Linotype machine.
Mr. Sayers. Of course you could not use that for the Printing Office of the Government?
Mr. Benedict. I guarantee that in the average daily newspaper set by the Linotype machine you find from 10 to 20 errors to every one you find in the Record, and you would lose almost entirely the typographical style which makes the Record the most beautiful and perfect daily publicaion of the world, while produced under greater difficulties than are known in other daily offices.

Tell us how you really feel Mr. Benedict.

Granted this is just one point of view, it's still an interesting insider's view of the Linotype and its real world issues.  There are plenty of sources out there that more clearly describe the problems with the Linotype (in particular the rivers) as well as the cost of error correction.  I just liked this source for its directness.

One Space is Just Wrong

"The space between sentences is a an aesthetic and functional choice, not a law."

That's the tag line on my Twitter account.  It's been my motto as I approach this issue.  It's my attempt to be fair and even-handed, and to avoid being preachy.  However as I learn more about this issue, I'm beginning to realize that it might be wrong.  Or at least incomplete.

When it comes to typography, I stand by it.  If you have the luxury of choosing your sentence spacing, by all means, choose whatever sentence spacing you find appropriate for your composition.  Wide spacing, or word spacing, a little wide or very wide, or even narrower than word spacing if you like.

But what I've learned is there is a very clear right answer on how many times to hit the space bar after a full stop.

We must use two spaces after a full stop.

It's odd that I'd say this, considering such brash and pedantic statements from the monospacers like Farhad Manjoo are what set me down this obsessive compulsive trail.  But unlike their reasons, which are clearly wrong and easily dismantled, I have a reason that is practical, and actually important.

First, let me be completely clear.  The printed space between sentences in a published work is not what I am talking about here.  I am only talking about the number of times you should hit the space bar after a sentence.  These things are not the same today, although they used to be.  On a typewriter they were the same thing.  On a Merganthaler Linotype hot metal typesetting machine, they were the same thing (although it was two different kinds of spaces).  But on computers, they are not. 

Computers can format your sentences however you like.  There's just one catch: computers must first know what a sentence is.

Wait, isn't that an easy one?  Actually, it is not.  The problem is that the meaning of a period is ambiguous.  It's not just a full stop.  It's also used to mark abbreviations.  And for initials.  And as a decimal point.  And after enumerations.  And as part of an ellipsis.  These things don't trip up human beings that often.  But for computers, deciding if that period is a full stop defies all attempts at a solution.  And there have been scores of scholarly papers on this very subject of sentence boundaries.  Let's look at a worst case scenario:

"Who's going?" "You and I. Smith is going too."

Is that "You and I." followed by "Smith is going too."?  Or is that referring to someone named "I. Smith"?  With no context, there's no way for even a human being to decide.  So for a complete solution we need a computer program that is capable of understanding context.  This is way beyond our current state of the art in computer software.

But that's just one example, right?  I mean, even people aren't perfect, so there must be an approach that's close enough?  Well, that depends on what you mean.  I've seem algorithms that claim to be successful 95% of the time or even 98% of the time.  Let's think about that - 98% means that your average article longer than 50 sentences is likely to have an ambiguous sentence boundary in it that the computer can't figure out.

So why do we care if a computer can parse what we say?  One practical reason is for machine translation.  Machines that are trying to translate what you are comm­unic­ating can do a much better job if they know what a sentence is.  There's also text-to-speech for the visually impaired (and others), which requires a knowledge of sentence boundaries to yield realistic inflection.  And of course it's useful for those who want wider sentence spacing.  But the larger reason is simply that we are trying to comm­uni­cate, and if a computer is going to mess it up, theres a chance a person might blow it too.

This whole problem could be solved if we only had an unambiguous full stop, rather than the confusing period.  But actually we do, or at least, we did.  For hundreds of years, it wasn't just professional printers that added extra space after sentences.  When students learned basic penmanship in school, they were also taught to add extra space between sentences.  There were no typewriters or computers.  All person-to-person comm­unic­ations before the typewriter were handwritten, and people penned their letters with extra space between sentences.

In other words, the unambiguous full stop is simply a period combined with extra space.  But we are losing this standard piece of punctuation.  We are losing it to technology.  We lost it to the poor formatting capabilities of the Linotype, and the expense of corrections.  We lost it to the general desire for faster and cheaper printing, and even the slight savings in paper.  We lost it to early web design standards that ignored the issue, because HTML was never meant to be so heavily typographic, and the designers didn't want to bother.

But that's all in the past.  Right now, we are losing it to a group of people who have declared war on the extra space.

No, I don't mean typographers.  You do often see claims that typographers everywhere have declared extra spacing to be wrong.  What you don't see is hoards of actual typographers saying that.  Sure you see some here and there.  But there's also quite a few typographers who don't think it's such a hard and fast rule.  And even a few who long for the days of wider sentence spacing.  Despite any claims, typographers are not the driving force in this war.

The real leaders of the crusade are the editors.  If you see someone complaining on line about this issue, by far the best guess is that they are an editor of some sort, and they are complaining about editing out extra spaces.  It's unfortunate that no one has bothered to tell them of the wonders of search-and-replace.  Or of requesting new features in their software if it doesn't do what they need.  Or of buying someone else's software.  All of these choices would alleviate the editor's pain without destroying a basic piece of punctuation.  But instead of fixing their software, they have chosen to bend the habits of the world to their will.

It's more than just unfortunate.  It's tragic.  Editors are entrusted with preserving our comm­unic­ations, with standardizing them.  And yet it is editors who, simply out of plain laziness or technological ignorance, are willing to cast aside the unambiguous full stop like it was nothing more than yesterday's newspaper, or this morning's toilet paper.

In print, the unambiguous full stop disappeared thanks to cost-cutting.  Luckily, we had typewriters there to keep it alive, and teach us all the two-space habit.  But now we're in the computer age.  Much software has learned it's lesson from typewriters, and those two spaces are still used and recognized in a wide number of software packages.  But unfortunately there are other software packages that don't understand.  They learned their lessons from a print industry, without understanding that the loss of extra spacing was simply a cost-cutting strategy.

The irony is that today, the costs that lead to the demise of wide sentence spacing in the print industry no longer apply.  Thanks to the two-space typing habit it's a trivial change to allow the print industry to reliably typeset sentences according to any desired style.  And it's trivial for translation software, and text to speech software to reliably detect sentences and use that information.

Ultimately we write so that we can communicate our ideas clearly and effectively.  And our most basic unit of comm­unic­ation is the sentence.  Isn't it worth providing a reliable way of deciding what is and is not a sentence?

On the other hand, we could all abandon that extra space and just leave it up to chance.  Because think of all the time those editors can save!

Dynamic Sentence Formatting for Blogger

Prior to this blog, I wrote an article on formatting sentences with HTML and CSS.  And that article itself has been formatted so that the viewer can dynamically control the sentence spacing.

Now I've made my first pass at doing the same thing in Blogger.  At the right, you should see controls for adjusting the size of the added sentence spacing.  And in my very limited testing, it works for me on Safari 5.

In a perfect world, which I'm working towards, but we're still not there, the editing process would automatically mark each sentence in it's own span, which is what I did by hand in that older article.  But I haven't had time to rewrite Blogger's post editor yet.  What I've done instead is relied on my so-called typewriter habit, and Blogger's idiosyncratic method of preserving extra spaces by trading them for non-breaking space entities ("&nbsp;").

I use javascript at page load time to look for sequences of period-space-&nbsp, and replace them with a span that wraps the space between sentences.  Ideally I'd mark each sentence, but this was a bit easier to code.  Then I modify the word-spacing just for those spans.  The controller at the right finds the appropriate value in the style sheet and modifies it.

It's not perfect.  The lines don't seem to re-wrap based on this change, and when the spacing is changed too much you'll end up with the right margin broken.  I think this could be a Safari or WebKit bug, because my original code in that older article would reflow as needed, but in that case I wasn't using justified text [update: reflow does work in Firefox][update 2: working now in Safari, see comments].  Another problem is that it could miss some sentences if you haven't been careful about where you place your tags at sentence boundaries: if there's a tag inserted between the space and the nbsp, it won't account for that (it can handle a single tag between the period and the space though).  An additional problem is that if you had for example some alt text of an image that had a period and a space and an nbsp, it would probably muck up your alt text.  But neither of the last two problems is at all common in practice (and this should still be considered an early attempt).

This method could easily be extended to any web pages besides blogger.  If you have a two space habit, the script could be modified to look for period-space-space instead of period-space-&nbsp.  This works because even though HTML doesn't preserve your spaces for display purposes, the browser does seem to preserve them internally.

In fact you could extend this further and attempt to modify any web content, regardless of the author's typing habits, and look for sentence boundaries with any period and space.  Unfortunately as I've discussed elsewhere, this is prone to errors, and you'd have to do significantly more checking (for abbreviations, initials, etc.) just to make it close to accurate.  Only full grammar parsing would do a truly acceptable job.

Let me also note that I originally tried to implement this as a Google gadget, and while that would simplify the process of others adding this feature to their blogs, I hit a little snag that the gadgets are remotely loaded, and the browsers frown upon javascript from one domain monkeying around with the DOM for parts of the document that come from some other domain.  The only way I found around this was to add the HTML directly.  If there's another way to accomplish this please let me know.

So how can you add this to your Blogger page too?

First, you have to add a bit of CSS.  Go to your blog's dashboard, select "Template" and then "Customize".  Then "Advanced", and in the list that appears to the right, scroll down to the bottom and select "Add CSS".  In the window that you get add the following:

.sntc_space { word-spacing: 0.25em; }

And then click "Apply to Blog". Next, you have to add the HTML-based gadget. Go back to the Blogger dashboard, and click layout. Click "Add a gadget" in the spot where you want the control to appear. From the list of gadgets select the one called "HTML/Javascript". Set the title to whatever text you want above your control (e.g. "My blog's sentence spacing"), and then past the following into the content:

<script>
var className='post-body';
var oldbox=null;
function init_sentence_spacing() {
  oldbox=document.getElementById('quarter_em_sentence')
  var spaced_elements;
  if (document.getElementsByClassName == undefined) {
    spaced_elements = [];
    var allElements = document.getElementsByTagName("*");
    var element;
    for (var i = 0; (element = allElements[i]) != null; i++) {
      var elementClass = element.className;
      if (elementClass && elementClass.indexOf(className) != -1 && hasClassName.test(elementClass))
      spaced_Elements.push(element);
    }
  } else {
    spaced_elements = document.getElementsByClassName(className);
  }
  var elem;
  for (var i=0; (elem = spaced_elements[i]) != null; i++) {
    var foo=elem.innerHTML;
    foo=foo.replace(/([.!?][")]*) &nbsp;([A-Z<("])/g,"$1<span class=sntc_space> </span>$2");
    foo=foo.replace(/([.!?][")]*)(<\/[^<>]*>) &nbsp;([A-Z<("])/g,"$1$2<span class=sntc_space> </span>$3");
    elem.innerHTML=foo;
  }
}
function change_sentence_spacing(value,box) {
  var CSSRules
  if (oldbox) {
    oldbox.style.backgroundColor="white";
  }
  box.style.backgroundColor="#40ff40";
  oldbox=box;
  if (document.all) {
    CSSRules='rules';
  } else if (document.getElementById) {
    CSSRules='cssRules';
  }
  for (var j=0; j<document.styleSheets.length; ++j) {
    if (document.styleSheets[j].href==null) {
      for (var i=0; i<document.styleSheets[j][CSSRules].length; ++i) {
        if (document.styleSheets[j][CSSRules][i].selectorText == 'span.sntc_space') {
          document.styleSheets[j][CSSRules][i].style['wordSpacing'] = value;
        }
      }
    }
  }
}
if(window.addEventListener) {
  window.addEventListener('load', init_sentence_spacing, false);
} else {
  window.attachEvent('onload', init_sentence_spacing);
}
</script>

<table rules=all cellpadding=2px>
<tr>
<td onclick="change_sentence_spacing('0em',this);">None</td>
<td onclick="change_sentence_spacing('0.125em',this);">Tiny</td>
<td id=quarter_em_sentence bgcolor="#40ff40" onclick="change_sentence_spacing('0.25em',this);">Small</td>
<td onclick="change_sentence_spacing('0.50em',this);">Medium</td>
<td onclick="change_sentence_spacing('0.75em',this);">Large</td>
<td onclick="change_sentence_spacing('1.25em',this);">Huge</td>
</tr>
</table>

Totally and perfectly simple, right?  Save the gadget contents and you're all set.  Now just press the space bar twice between sentences in the Blogger post editor and your readers will be able to control how they view your sentence formatting.

Note that with this setup, the default extra space is a quarter em (very conservative), and that this corresponds to the "Small" button in the control.  If you want to change this default, pick a different value for ".sntc_space" in the CSS, and move the "id=quarter_em_sentence" piece to the correct table element for the value you've made your default (but don't rename that id unless you also fix the code that looks for it; I guess that was a poor choice to name that id but I don't feel like correcting it at the moment).  You can also change the values or labels in the table to anything you'd like.

19th Century Typewriting and Handwriting Rules

I've done a bit of searching of old books for spacing rules used on typewriters.  There's not much out there.  In typesetting, sources are consistent in either recom­mending an em-quadrat between sentences, or making no mention of sentence spacing at all.  There was one reference I've found (and can't find in my notes on, grrr), which had the recom­men­dation for spacing that you should simply pick up any book of the day and you could learn everything you need to know by looking at it.  I've also found a handwriting book from 1873 (Analysis of Letter Writing, by Calvin Townsend) which describes desired spacing in handwriting on page 19:

  The rule is, to leave space sufficient to write the minimum m between the words, of the same size of that letter used in the body of your writing.  [...]
  After an interrogation or exclamation point, and following the period, space enough should be left to write a double m.

Note too the date, 1873 was the same year the first 1000 typewriters in the world went into production, so this wide sentence spacing can (once again) not be blamed on typewriters.

But for the most part, in penmanship manuals and especially in typewriting manuals I'm finding this topic simply gets no mention at all.  My belief is that wide spacing was such an ingrained habit from the time people learned to write, that it was simply automatic.

So I was happy to find this tidbit from The Phonographic Magazine, Volume 12 (1898), By Jerome Bird Howard, on pages 206-207:

TYPEWRITER SPACING AFTER PUNCTUATION MARKS.

  Are there any stated rules for spacing after punctuation marks in typewriting?  I notice that some writers put a space after a comma, and two spaces after a period, while others do not put any extra space after a comma and only one space after a period.  Which is correct?
  Answer.—It is our observation that in the best specimens of typewritten work there is always a space following a comma, and two spaces following a period.

I like this because the wide sentence spacing is assumed in either choice without any analysis at all.  But also because it demonstrates that if anything, people felt that typewriter spacing might need to be less than traditional typeset spacing, rather than more.